Leather lubricating process and composition

ABSTRACT

Low-oil-content, fully lubricated leather is produced by (1) treatment of leather with water emulsions of mixtures of alkanolamine soaps, oils, surfactants having HLB values between 2 and 6, and coupling solvents; and (2) acidification of the leather.

Ilnited States Patent emwall [151 3,656,8M 51 pt. 1,197

LEATHER LUBRICATING PROCESS AND COMPOSITION Robert W. Hemwall, Chatham, NJ.

Assignee: Shell Oil Company, New York, NY.

Filed: June 2, 1969 Appl. No.: 829,729

Inventor:

US. Cl ..8/94.23, 8/94.22, 252/857 Int. Cl Field of Search ..8/94.22, 94.23

References Cited FOREIGN PATENTS OR APPLICATIONS Great Britain OTHER PUBLICATIONS M. Lesser Soap & Sanitary Chemicals March 1948 W. J. Hopkins (I) Journal of the American Leather Chemists Assoc. Vol. LXIINo. 3 March 1967 W. J. Hopkins (ll) Journal of the American Leather Chemists Association Vol. 61 No. 8 Aug. 1966 Primary Examiner-George F Lesmes Assistant Examiner-B. Bettis Att0meyWilliam H. Benz [5 7] ABSTRACT 5 Claims, No Drawings BACKGROUND OF THE INVENTION When unlubricated wet leather is allowed to dry it will become hard and stiff because of cohesion of the leather fibers. The principal purpose of such a leather lubricating process as conventional fatliquoring is toprevent or control this cohesion so that the leather will be strong and of the desired degree of flexibility or softness.

Commercial fatliquors contain one or more animal and/or vegetable oils together with one or more wetting or emulsifying agents of the typesthat promote oil-in-water emulsions. These agents have little or no lubricating value of their own. They act merely as coupling agents that assist the emulsified oils to enter the wet leather and coat the leather fibers, thus preventing cohesion thereof when the leather dries. Particularly with the stronger emulsifiers this action is apparently reversible. In consequence, when the dried, fatliquored leather is rewetted by water the emulsifier facilitates the displacement of the leather lubricant from the fiber surfaces. When this happens the leather will dry hard even through large quantities, e.g., -20 percent w, of lubricant have been used.

Because of the nature of conventional fatliquors, they do not permit the manufacture of an adequately lubricated lowoil-content leather. Recent trends in shoe construction, especially for waterproof shoes and boots, are directed toward direct-molded or vulcanized soles wherein the sole is attached directly to the shoe upper without stitching, so a strong bond between the sole and upper is acquired. Since the bond strength is inversely related to the oil content of the leather, a

very low oil-content leather is desired.

A second problem with conventionally lubricated leather is that the hydrophillic wetting and emulsifying agents in conventional fatliquors adversely affect all waterproofing compounds. With the market for waterproof leather goods increasing greatly, a substitute for fatliquors which would permit water-proofing and produce an adequately lubricated low-oil leather is highly desirable.

One method of producing well lubricated leather with low oil content is described in U.S. Pat. No. 3,035,882 to von Fuchs, May 22, 1962. Here leather sides are individually dipped in a water-immiscible organic solution of higher alkenylsuccinic acid. While this method can produce lubricated leather with an oil content of about 1 percent wt, it has several serious shortcomings.

1. Each side of leather must be handled individually.

2. It is a totally non-aqueous step in an otherwise all-aqueous tanning processes.

3. Pick-up of lubricant is regulated by residual water content of the leather and is therefore very difficult to control.

4. Slight over-lubrication often causes an extremely loose break in the leather.

These disadvantages are in part corrected by the process described in The Journal of the Americal Leather Chemists Association Volume 61 (1966), at page 384, wherein an oil-inwater emulsion of alkenylsuccinic acids, produced by adding coupling-solvent, was used as lubricant. To prevent phasing,

however, a coupling solvent-to-lubricant ratio of from about 40/1 to about 5/1 must be used. This use of large amounts of generally expensive coupling solvent, only a portion of which is recoverable, makes this process unacceptably expensive.

STATEMENT OF THE INVENTION It has now been found that low-oil-content, fully lubricated leather results from treatment of leather with mixtures comprising alkanolamine soaps, oils, relatively lipophilic surfac-- l. The coupling solvent-to-lubricant ratio may be reduced to 2/1 or less without phase separation.

2. All residues left in the leather following acidification are hydrophobic.

3. Emulsion and product leather characteristics can be varied by changing the lipophilic surfactant blend.

DETAILED DESCRIPTION OF THE INVENTION Leather lubrication mixtures useful according to this invention consist of mixtures comprising the following materials:

alkanolamine soaps of organic acids oils relatively lipophilic surfactants coupling solvents.-

The alkanolamine soaps may be added to the mixture as such or may be formed in the mixture by the addition of alkanolarnines and organic acids. Although the addition of soaps as such is suitable, the in situ generation method is generally preferred.

Suitable alkanolamines comprise the mono-, di-, and trialkanolamines having from about two to about 10 carbon atoms in each alkanol group. Preferred among these are the diand trialkanolamines having from about two to about four carbon atoms in each alkanol group, with triethanolamine comprising the more preferred amines.

Organic acids useful for preparing alkanolamine soaps for use in this invention comprise saturated and unsaturated monobasic and polybasic organic acids having from about 10 to about 30 carbon atoms per molecule. These acids may be provided in a pure state or as mixtures. A generally preferred class among these acids are the aliphatic acids, such as for example, the saturated fatty acids, unsaturated fatty acids, alkyl and alkenyl-substituted saturated dibasic acids, and alkyl and alkenyl-substituted unsaturated dibasic acids.

Preferred acids comprise the unsaturated fatty acids having from about 15 to about 25 carbon atoms per molecule and the alkenyl-substituted saturated dibasic acids. Preferred unsaturated fatty acids comprise palmitoleic acid, oleic acid, linoleic acid, and linolenic acid. Preferred alkenyl-substituted saturated dibasic acids comprise the intermediate and higher alkenylsuccinic acids.

Highly preferred acids comprise oleic acid and iso-octadecenylsuccini acid, with iso-octadecenylsuccinic acid being more preferred, especially the hydrolyzed reaction product of propylene hexamer and maleic anhydride.

Oils useful in the lubricating mixtures according to this invention comprise both mineral oils and animal and vegetable oils. Mineral oils are generally preferred.

Surfactants useful in these lubricating mixtures comprise ionic and anionic surfactants which are relatively liphohilic in character. The desired degree of lypophilicity can be expressed by the HLH number of the surfactant. I-ILB number or l-lydrophile-Lipophile balance number is a measure of the balance in the size and strength of the two opposing groups in a surfactant. This method is explained in Osipow, Surface Chemistry (ACS Monograph Series 153, 1962) page 311. Surfactants having HLB numbers of from about 1.5 to about 8 are suitable.

Surfactants in this I-ILB range are polar enough to act as coupling agents between non-polar oils and polar protein molecules but yet are hydrophobic enough to be generally uneffected by water rinsing and to cause minimal interference with waterproofing treatments. Surfactants having l-ILB numbers of from about 2 to about 6 are preferred. Illustrative of the surfactants which comprise these preferred surfactants are sorbitan oleates, sorbitan stearates, polyoxypropylene modified fatty acid esters, polypropylene glycol fatty acid esters and polyoxyethylene alcohols. Among these preferred materials, sorbitan sesquioleate, sorbitan monooleate, sorbitan tristearate, and sorbitan monostearate are preferred, with sorbitan sesquioleate being especially preferred.

Polar hydrocarbon solvents are generally suitable coupling solvents. Preferred coupling solvents comprise polyols and polyoxyalkylene glycol ethers, such as, for example, ethylene glycol, propylene glycol, isobutylene glycol, amylene glycol, hexylene glycol, octylene glycol, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether and dipropylene glycol monoamyl ether. Most preferred coupling solvents comprise hexylene glycol and diethyleneglycol monobutyl ether.

It is acceptable to separately add the materials comprising the lubricating mixture, oils, alkanolamine soaps, etc., as herein described, to the leather treating apparatus. lt is preferred, however, to combine the lubricant components prior to adding them to the leather.

Although the proportions may be varied somewhat depending on the sepecific components used and the specific properties desired of the treated leather, acceptable lubricants, according to the invention generally comprise the following proportions of components:

Preferred lubricating compositions comprise:

Dior tri-alkanolamines having from about 2 to about 4 carbon atoms per alkanol group Unsaturated fatty acids or alkenyl substituted unsaturated dibasic acids 0.5-3.0 parts by weight 0.3-1.8 parts Oils 1 part Surfactants having HLB numbers of from about 2 to about 6 0.5-1.8 parts Polyols or polyoxyalkylcnc glycol ethers 1.5-8 parts More preferred lubricating compositions comprise:

Triethanolamine 0.7-2.0 parts by weight lso-octadeccnylsuccinic acid 0.5-1.2 parts Light mineral oil l part Sorbitan sesquioleate 0.7-1.3 parts Hexylene glycol 2-8 parts Most preferred lubricating compositions comprise:

Triethanolamine 1.0-1.6 parts by weight lso-octadecenylsuccinic acid 0.8-1.0 parts Light mineral oil 1 part Sorbitan sesquiolcate 0.85-1.15 parts Hcxylene glycol 4-7 parts The lubrication mixtures according to this invention are suitably applied to leather as an emulsion in water. In one application, leather is floated in water and then the lubrication mixture is added to the water with mixing, whereupon the lubricating mixture immediately forms an emulsion in the water.

The amount of lubricating mixture added can vary widely. Generally, an amount equivalent to from about 1 percent to about 10 percent of the blue-shaved weight of the leather is acceptable, with amounts from about 2 percent wt to about 7 percent wt being preferred.

A water emulsion of the lubricating mixture according to the invention generally has a pH of about 6 to about 7. As the lubricant is absorbed into the fiber matrix of the leather the pH of the liquid drops from this pH range to a pH in the range of from about 4 to about 6. It is believed, although not understood with certainty, that the alkanolamine soaps are neutralized by protein-bound stronger acids present in the leather from prior processing steps. This neutralization causes the emulsion to become locally unstable in the leather allowing the oils and surfactants to coat the leather fibers.

Acidification of the leather and of the liquid in which the leather is floated, following absorption of the emulsion by the leather is highly desirable. When the pH of the solution and the leather is brought to about 3.0 to about 4.0, by acid addition, the neutralization of the alkanolamine soaps is completed so that no hydrophillic residue remains in the leather.

While any acid having a pKa less than about 5 can be used for this neutralization, preferred acids comprise those which have pKa values from about 3 to about 5, such as, for example, formic acid, acetic acid, benzoic acid, citric acid, and lactic acid. Very preferred acids comprise formic acids.

The amount of acid added can vary widely depending on the amount of alkanolamine soap present. Generally from about 0.5 percent wt to about 2.5 percent wt, based on the blueshaved weight of leather treated, is sufficient to bring the pH within the desired final range.

The invention will be further illustrated by the following examples:

EXAMPLE I lso-octadecenylsuccinic acid 892w Sorbitan sesquioleate 10% Light mineral oil 10% Triethanolamine 14% Hexylene glycol 58% (Solvent to lubricant ratio equals about 2/1) The lubricant emulsified spontaneously. The container was tumbled for 45 minutes during which time the emulsion was completely absorbed by the leather. One percent formic acid was then added and the container was tumbled for 30 minutes.

When the lubricant was first added to the container the system pH was 6.3. After absorption of the emulsion into the leather the pH was 5.4. The final pH, after acid addition and absorption, was 3.8.

Following overnight mulling and drying, the leather was mellow, full, and round, with an exceptionally fine break. The residual lubricants were all hydrophobic and constituted about 1 percent of the initial sample weight.

Identical experiments carried out at 70 and 120 F. gave very similar results.

EXAMPLE 11 Using the procedures, amounts, and lubricant of Example 1, samples of cattlehide retanned with lignosulfonate and melamine resins, and a sample of chrome-tanned sheepskin were lubricated. In all cases, soft, supple leathers were produced.

EXAMPLE 111 A sample of cattlehide, identical to the leather in Example 1 was placed in a container with a percent water float at room temperature. To the container was added 2.3 percent of a lubrication mixture which comprised:

lso-octadecenylsuccinic acid 15.2 Sorbitan sesquioleatc 13.1 Light mineral oil 15.2 Triethanol amine 13.0 Hexylene glycol 43.5

(Solvent to lubricant ratio equals l/l.)

This lubricating material emulsified at once with water and was completely absorbed by the leather in about 2 hours.

EXAMPLE IV In a series of larger scale tests sides of chrome-tanned, vegetable-retanned, dyed, cattlehide grain leather were lubricated using the lubricant of Example I and conventional tannery apparatus. The amount of lubricant mixture was varied from 2.45 percent (0.7 percent actual lubricant) to 3.85 percent (1.1 percent actual lubricant) to 5.25 percent (1.5 percent actual lubricant). In all cases the leather was drummed for 30 minutes and then acidified with formic acid to pH about 3.4 3.5. In all cases, well-lubricated leather was produced. In no case, however, was leather with a loose break, indicative of over lubrication, observed.

1 claim as my invention:

1. A process for lubricating leather which comprises the steps of l treating the leather with an aqueous emulsion of a lubricating composition consisting essentially of one part by weight oil, from about 0.8 to about 4.8 parts by weight of the alkanolamine soaps resulting from the reaction of dior trialkanolamines having from about two to about four carbon atoms per alkanol group with to 30 carbon atom organic acids selected from the group consisting of unsaturated fatty acids and alkenyl substituted saturated dibasic acids, from about 0.5 to about 1.8 parts by weight lipophilic surfactants having HLB numbers from about 2 to about 6, and from about 1.5 to about'8 parts by weight of a coupling solvent selected from the group consisting of polyols and polyoxyalkylene glycol ethers; and (2) acidifying the leather.

2. The process according to claim 1 wherein the lubricating composition is used in amount equivalent to from about l percent to about 10 percent of the blue-shaved weight of the leather treated.

3. The process according to claim 2 wherein the leather is acidified to a final pH of from about 3 to about 4.

4. The process according to claim 3 wherein as lubricating composition is used the lubricating composition according to claim 4 in amount equivalent to from about 2 percent to about 7 percent of the blue-shaved of the leather treated.

5. The process according to claim 3 wherein the leather is acidified with formic acid. 

2. The process according to claim 1 wherein the lubricating composition is used in amount equivalent to from about 1 percent to about 10 percent of the blue-shaved weight of the leather treated.
 3. The process according to claim 2 wherein the leather is acidified to a final pH of from about 3 to about
 4. 4. The process according to claim 3 wherein as lubricating composition is used the lubricating composition according to claim 4 in amount equivalent to from about 2 percent to about 7 percent of the blue-shaved of the leather treated.
 5. The process according to claim 3 wherein the leather is acidified with formic acid. 